Liquid development apparatus for electrophotography

ABSTRACT

An electrophotographic liquid development apparatus comprising developing electrodes positioned face to face with a thin clearance therebetween to receive an electrophotographic material bearing an electrostatic latent image, means for supplying liquid development agent to the thin clearance to develop the latent image, and switching means in circuit with the developing electrode which directly faces the electrostatic latent image, the switching means being provided with at least two circuit paths to change the grounding resistance according to an original image used to form the latent image, wherein if the latent image comprises a linear drawing, a high resistance circuit path is employed and if the latent image is of a continuously toned nature, a low resistance circuit path is employed as the medium through which the developing electrode is grounded.

United States Patent 119 1111 3,822,670 Sato et al. 1 July 9, 1974 [5 1 LIQUID DEVELOPMENT APPARATUS FOR 3,599,605 8/1971 Ralston et a1 118/637 RAP 3,601,092 8/1971 Satomi 118/637 ELECTROPHOTQG. HY 3,674,532 7/1972 Morse 117/17.5 1 Inventors: Masanuchl .1 Takahashl; 3,685,907 8/1972 Sato et a1 118/D1G. 23 Takao Komaki; Satom Honjo, all of I Asaka, Japan. Pn'mary Examiner-Mervin Stein 73 A I F Ph t F] C Ltd Assistant Examiner-Leo Millstein sslgnee gfi s g 3; 0 Attorney, Agent, or Firm-Gerald J. Ferguson, Jr.; .10-

seph J. Baker; J. T. Martin [22] Filed: 28, 1971 [21] Appl. No.: 213,089 ABSTRACT An electrophotographic liquid development apparatus comprising developing electrodes positioned face to [30] Foregn Apphcatmn 'Pnomy Data face with a thin clearance therebetween to receive an Dec. 28, Japan electrophotographic material bearing an electrostatic latent image, means for supplying liquid development [52] Cl 118/637 agent to the thin clearance to develop the latent im- 1 1 Cl g 15/00 age, and switching means in circuit with the develop- [5 1 5 LE ing electrode which directly faces the electrostatic 1a- [58] held 0 63? l0 tent image, the switching means being provided with l D at least two circuit paths to change the grounding resistance according to an original image used to form [56] References cued the latent image, wherein if the latent image comprises UNITED STATES PATENTS a linear drawing, a high resistance circuit path is em- 2,913,353 11/1959 Mayer et a1 117/37 ployed and if the latent image is of a continuously 3,328,193 6/1967 Oliphant et a1. 1 17/37 toned nature, a low resistance circuit path is employed 3,345,925 Ostensen as the medium through the developing elec- 3,368,894 2/1968 Matkan et a1... 96/1 node is grounded 9 3,411,482 l1/1968 Brodie 118/637 3,435,802 4/1969 Nail 118/637 3 Claims, 9 Drawing Figures 20 2O 2O 2O PATENTEDM 91914 SHEEI 1 OF 3 FIG. i

PATENTED JUL 91974 SHEET 2 0F 3 FIG.4

FIG. 6

FIG. 7

PATENTEU-M 91 14 SREET 3 OF 3 FIG. 9

'1 LIQUID DEVELOPMENT APPARATUS FOR ELECTROPHOTOGRAPHY BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid development apparatus for an electrophotographic material possessin g an electrostatic latent image, and especially to a liquid development apparatus capable of selectively forming excellently reproduced continuously toned images or line images of reduced background density (or fog).

face of the electronic photographic material is very thickness of the fine lines as ranges between several 1 100 ,u. and 1 mm, the adherence of the toners by edge effect can only produce images of high intensity. Of course, in order to develop a continuously tone image, it is essential that the toner adhere in an extensive are and in proper responseto the electric charge intensity of the electrostatical latent images. For continuous tone images, the edge effect turns out to be detrimental to true reproduction of the continuous tone image because only the end territory of the electrically charged field is developed with strong intensity.

In order to prevent generation of edge effect and to afford improved adherence of latentimages in proportion to the electric charge quantities, it is known to place a well-grounded metallic plate (developing electrode) in the direct vicinity of the latent images so the plate faces the latent images. This conventional method serves to solve the aforesaid problem. However,.when the developing electrode is located in the neighbourhood of the latent image, upon development of line images, the toner is inclined to adhere to electric charges existing in the non-image bearing part also, tending to tones of the image. Occasionally, for the purposeof realizing regeneration of the continuously changing tones of the images, the developing electrode is allowed to be located in the vicinity of the latent image intentionally inviting line images with the accompaniment of the fogging effect.

SUMMARY OF THE INVENTION In this invention, an electrophotographic liquid development apparatus is offered which prevents the above mentioned disadvantages, enabling preferable effect for development with continuous toned-images and development of line images.

The distinctive features of this invention relate to the electrophotographic development apparatus wherein:

1. when line images are to be developed the developing electrode located in the direct vicinity of the latent images is electrically insulated or grounded by means of a high resistivity element to generate an electric field oriented in the opposite direction to that generated in the image part in the non-image bearing territory, i.e. toner is prevented from adhering to the non-image bearing territory by eliminating the electric field generated through residual electric charge existing in the non-image bearing territory; and

2. when continuously toned images are to be developed, the developing electrode is grounded in a direct manner through a medium of low resistance to allow images in proportion to the quantity of electrical charge on the latent images between the developing electrode and the latent image surface to be formed, thereby enabling continuously toned images to be obtained by means of allowing toner to adhere to the latent image proportionally to the quantity of electrical charge.

BRIEF EXPLANATION OF DRAWINGS FIG. 1 represents side sectional view of one embodiment of the present invention.

FIG. 2 represents side sectional view of a second embodiment of the present invention.

FIG. 3 represents sectional view of a third embodiment of the present invention.

FIG. 4 through FIG. 7 represent side elevations of portions of the present invention which function to electrically lift up the development rollers from the ground.

FIG. 8 represents a preferred electric circuit diagram for use in the apparatus of the present invention.

FIG. 9 represents a copying apparatus having a developing apparatus of this invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention shall now be explained in detail with reference to the attached drawings.

FIG. 1 represents an outlined side sectional view of a practical one embodiment of the present invention. A guide shell 10 made of metallic gauze is attached to a side board (not shown) by means of supporting brackets 11. The shell 10 is provided with a configuration of a circular are viewed from the transverse direction, and it is grounded by any known means. On top of the guide shell 10 is a dielectric developing electrode 12 attached to the side board or to the guide shell 10 by fixing means, in an electrically insulated manner with respect to the guide shell 10, the electrode 12 being located against the guide shell 10 keeping a small clearance between them, for instance, as small as 0.5 2 mm.

Inthe region between guide shell 10 and developing electrode 12 there is constantly supplied by any known means the developing liquid in which the charged particles, that is to say, the toner finely distributed in an insulating carrier liquid, whereby the electrostatical latent image of the electrophotographic material introduced in this region is developed. The developing electrode 12 is electrically connected with switch 13, and upon contact of contact piece 1.3- of the switch 13 with a contact point 13-1, the developing electrode 12 is allowed to be grounded in a direct manner and upon contact of piece 13-() with contact piece 13-2, grounding is accomplished through resistance element R.

At both ends of the guide shell 10, there are located a pair of feeding rollers 14 and a pair of discharging rollers 15, these two pairs of rollers being supported by the side board and made to rotate in the direction shown by the arrows 16 by driving means. These pairs of feeding rollers 14 as well as discharging rollers may be of metallic materials or insulating materials.

The resistance R element is provided with a resistance of more than 10 0, however, it can be extended up to infinity, that is to say, it may be insulated from the ground. When the electrophotographic material provided with a latent image is introduced in the pair of the feeding rollers 14 in the direction shown by an arrow 17 with the latent image surface turned upward, it is nipped by rollers 14 and displaced between the guide shell 10 and developed by the toner in the developing liquid, and thereafter fed out by the nipping action of rollers 15.

On this occasion, when the electrophotographic material is provided with line images and when the contact piece 134) of the switch 13 is preliminarily placed in contact with the contact point 13-2, then while development upon the developing electrode surface which is facing against the imaged part of the latent image surface, an electric charge whose polarity is opposite to that of the electric charge of the latent image is induced. The developing electrode provided with an grounding resistance of high value 10 to D is at a finite potential. As the development proceeds the toner deposits on the latent image and an occurred developing current flows to the ground through the grounding resistance whereby the developing electrode is kept at a potential. The electric field would not be generated by the remaining electric charge on the background area of the latent image and accordingly the toner is hardly adhered to the non-image bearing part, thus producing line images of reduced fogging and satisfactory clarify.

On the other hand, when the electrophotographic material is provided with continuously toned images, then contact piece 13-0 of switch 13 is initially contacted with the contact point 13-1, and the electric charge with an opposite polarity to that of the latent image generated on the developing electrode surface which is facing against the latent images becomes proportional to the electric charge quantity of the latent image and the electric charge having the same polarity as the latent image generated in accompaniment of the above phenomenon flown to the ground through the switch 13 via line 13-1. In this case, on the developing electrode 12, an electric charge having polarity opposite to that of the latent image exists in proportion to the electric charge quantity of the latent image, an electric field proportional to the electric charge quantity of the latent image is produced between the electrophotographic material and the developing electrode 12 and thus, the toner adheres to the latent image in proportion to the electric discharge quantity of the latent images, giving an excellent image of continuously changing tone.

The electrophotography liquid development apparatus represented in FIG. 1 provides by means of only a simple flip of a switch, line images of reduced fogging and excellent continuous tone images.

FIG. 2 represents side sectional view of another embodiment of the present invention.

In FIG. 2, an even number of pairs of rollers, though it will be obvious an odd number of pairs could be used, (in this illustration 4 pairs of rollers are shown) consisting of grounded driving rollers 20 and insulated developing rollers 21 are supported by a side board (not illustrated) and made to rotate by a proper driving mechanism in the direction of arrows 24. The driving rollers 20 and developing rollers 21 are made of metallic material and the driving rollers 20 and developing rollers 21 are rotated keeping a small gap therebetween, e.g. of ranging from 0.1 to 1 mm.

The electrophotographic material is inserted between the driving rollers 23 and the developing rollers 21 in the direction shown by an arrow 25, and developing liquid is supplied to the developing rollers 21 by any known means. The developing rollers 21 is grounded through a very large resistance or insulated from the ground as shown in FIG. 4 through FIG. 7. Further,

each individual developing roller is connected electrically to the other developing rollers and is also connected to the contact piece 13-0 of the switch 13. Contact point 13-1 of switch 13 is directly connected to ground and contact point 13-2 is connected to ground by means of resistance R. The resistance R is provided with the same value as shown in FIG. 1.

In operation using the embodiment of FIG. 2, when linear latent images are developed the contact piece 13-0 of the switch 13 is connected to contact point 13-2, and when continuous tone images are developed, it is connected with contact point 13-1. In this manner, excellent line images as well as continuous tone images, as represented in the embodiment shown in FIG. 1, can be developed at will.

FIG. 3 represents side sectional view of a further embodiment of the present invention. This particular embodiment featrues developing rollers at the latter half of the developing operation which are connected wholly and directly with the ground even for the development of line images. In the embodiment shown in FIG. 3 excellent results can be obtained as with the embodiments of FIGS. 1 and 2.

It should be noted that the undesirable background potential (residual potential) decays gradually during development, the biasing effect of the development electrode is often very important at the initial stage of development. In the present embodiment shown in FIG. 3, the substantial portion of development is considered to have finished under the first three roller pairs. Under the remaining three pairs 31 only supplementary development effect is expected such as between solid area coverage, etc.

In the embodiments shown in FIG. 1, FIG. 2, and

FIG. 3, contact point 13-1 of the switch 13 is connected directly to ground, however, if the connection is made by means of a comparatively low resistance the same high quality images are available as in the case when the connection is made directly.

FIGS. 4-7 illustrate means of electrically insulating the developing rollers 21 from the side board which supports in a practical manner well suited for the embodiments of the present invention shown in FIGS. 2 and 3.

In FIG. 4, in bearing slots 41 located in the grounded metallic side board 40 the bearing shaft 42 of the developing rollers 21 are covered with an insulating material 43, thus insulating the developing rollers 21. The material 43 can be in a pipe-like form and made of an insulating resin, e.g., polyvinyl chloride, polyamide, polyethylene, polypropylene, acrylic resin, Bakelite and other similar synthetic resins. However, it is acceptable to coat the shaft 42 with an insulating paint of such as a styrene-vinylor epoxide family paint, in place of pipe FIG. 5 represents an embodiment of the present invention in which the inside of the developing roller bearing slots 41 located on the grounded metallic side board 40 there is provided a thin layer 50 of the same material as employed for pipe '43 shown in FIG. 4, and the shafts 42 of the developing rollers 21 and side board 40 are thus insulated.

FIG. 6 represents an embodiment of the invention in which, the lower part 60 of the side board 40 is constructed of a metallic material and grounded and the bearing shafts 61 of driving rollers 20 are installed to support the driving rollers 20. However, the upper part 62 of the side board 40 is made of an insulating material, the e.g. of the same material as pipe 43 shown in FIG. 4. Upper part 62 accommodates the developing roller bearing shafts 63 and by means of supporting the developing rollers 21 these developing rollers 21 are insulated from the ground.

FIG. 7 represents a further practical example in which, the lower part 70 of the side board 40 is constructed of metallic material to be grounded and bearing shafts 71 of the driving rollers 20 support the driving rollers 20. An intermediate insulating material layer 72 separates the upper part 73 of the side board 40 from lower part 70, and thus the upper part 73 is constructed of a metallic material. Developing roller bearing shafts 74 are installed to support the developing rollers 21.

The insulating layer 72 can be of the same material as pipe 43 shown in FIG. 4. With the strength of the construction as represented in FIG. 7, by means of connecting any proper position of the lower part 70 of the side board with the ground all the driving rollers become grounded, and by I means of connecting any proper position of the upper part 73 of the side board with the contact point of the switch, all the developing rollers become connected with the contact piece of the switch, thus giving pronounced advantages.

Further, as in the case of the embodiments shown in FIG. 1'FIG. 3, for the original line images the developing electrode is grounded'through high resistance and for original continuous tone images, a low resistance is employed.

However, even for original line images, line images of thicker lines and half tone images are often involved and sometimes different matrix colors and intensities are also involved. It is thus advisable, without fixing the value R indicated in FIG. 1 through FIG. 3 at a constant figure, to make R variable in the range from 0 as shown in FIG. 8. I

Similarly, even for continuously toned images, as the differences'of intensities and colors of the matrix cause different residual electrical potentials, it is advisable to connect the developing electrode with the ground resistance lower than 10 9, without connecting it directly, and to make the grounding resistance variable in the range of O to 10 0 as shown by R in FIG. 8.

FIG. 9 is a sectional side view of an apparatus comprising the liquid developmentapparatus of the present invention. In FIG. 9, the elongated web of electrophotographic paper is loaded in a roll as shown by numeral 9. The paper is fed from the roll 9 through a pair of rollers 91, and is cut to a constant length by a cutter 92. The cut paper is transported along the dotted line shown in FIG. 9. The paper is reformed its curl at an apparatus 93. This apparatus 93 comprises a pair of rollers, an endless belt spread on these rollers and a roller which is placed between them. The paper is fed between the endless belt and the last roller and then is put on an endless belt 94 provided with a lot of holes of l to 3 mm in diameter uniformly. A vacuum absorbing apparatus 95 is provided behind the endless belt 94. The sheet is transported adhering to the endless belt, while the sheet is uniformly charged by the corona discharge apparatus and imagewise exposed through an optical instrument. Then the sheet is turned to right by the apparatus 98. This latent image bearing sheet is supplied with insulating liquid such as kerosene at stage from a nozzle 101 provided between two pairs of nip rollers, and is developed at the stage 90. The development stage 90 is comprising fine pairs of nip rollers which act as above-described referring FIG. 3, three nozzles 99 disposed above the middle three developing rollers, and a vessel to receive an excess developer. The first three developing rollers are alternatively switched to direct ground or to ground through resistance. The last two'developing rollers are directly grounded. The developer in the vessel is returned to the nozzles 99 by a pump not shown in the figure. The developed sheet is rinsed at stage 110. From a nozzle 111 a rinse liquid is fed onto the sheet between two pairs of rollers and wash away the excess toner from the image surface. The liquid is preferably of higher volatilization than that of the carrier of the developer. The wet sheet is squeezed by a pair rollers 112, 113. According to this apparatus, a line image of reduced fogging and an excellent continuous tone image is obtained by means of only a simple flip of a switch.

Numerous modifications of the invention will become apparent to one of ordinary skill in the art upon reading the foregoing disclosure. During such a reading it will be evident that this invention provides a unique liquid development apparatus for electrophotography for accomplishing the objects and advantages herein stated.

What is claimed is:

1. An electrophotographic liquid development apparatus comprising a plurality of developing electrodes positioned face to face with a moving electrophotographic sheet material bearing an electrostatic latent image with a thin clearance therebetween, said plurality of developing electrodes being divided into first and second groups, each group comprising at least one developing electrode where said moving electrophotographic sheet material first encounters said first group, means for supplying liquid developing agent to the said thin clearance to develop the said latent image, a first grounding resistance connected to ground, a second grounding resistance connected to ground substantially larger than said first grounding resistance, and switching means connected between said first group of developing electrodes and said ground resistances for changing the grounding resistance according to an original image used to form said latent image, wherein if said latent image substantially comprises a linear drawing, said second grounding resistance is employed and if said latent image is of a continuously toned nature, said first grounding resistance is employed as the medium through which the developing electrode is grounded, both of the circuit paths respectively including said first and second grounding resistances including no sources of electric potential, said second group of developing electrodes being directly conneqted to said first grounding resistance so that when said latent image resistance is zero ohms. 

1. An electrophotographic liquid development apparatus comprising a plurality of developing electrodes positioned face to face with a moving electrophotographic sheet material bearing an electrostatic latent image with a thin clearance therebetween, said plurality of developing electrodes being divided into first and second groups, each group comprising at least one developing electrode where said moving electrophotographic sheet material first encounters said first group, means for supplying liquid developing agent to the said thin clearance to develop the said latent image, a first grounding resistance connected to ground, a second grounding resistance connected to ground substantially larger than said first grounding resistance, and switching means connected between said first group of developing electrodes and said ground resistances for changing the grounding resistance according to an original image used to form said latent image, wherein if said latent image substantially comprises a linear drawing, said second grounding resistance is employed and if said latent image is of a continuously toned nature, said first grounding resistance is employed as the medium through which the developing electrode is grounded, both of the circuit paths respectively including said first and second grounding resistances including no sources of electric potential, said second group of developing electrodes being directly conneqted to said first grounding resistance so that when said latent image substantially comprises said linear drawing, the first group of developing electrodes, which are connected to said second grounding resistance through said switching means, lessen the tendency of background fog to be developed while said second group of development electrodes effect supplemental development of said latter latent image after the residual background charge has substantially decayed.
 2. Apparatus as in claim 1 wherein said first grounding resistance is less than 106 ohms and where said second grounding resistance is greater than 106 ohms.
 3. Apparatus as in claim 2 where said first grounding resistance is zero ohms. 